a super mesh situation arises when one mesh contains a current source in its path. the way to work around it is to go around the "super mesh" and apply kvl in the supermesh. the super mesh is a loop formed by those mesh tht had the current source common to them. this way the voltage across the current source need not be taken
such a method is usually not necessary. one can assume a voltage v across the current source and then write to normal mesh equation and then eliminate the assumed variable v between the 2 equations.. the results are the same

hmmm webpage for supermeshes and supernodes i havnt come across.. ll post it as soon as i come across one
meanwhile if you hav access to books you may see Engineering Circuit Analysis by Hayt and Kemmerly. it does hav a discussion on supernodes and supermeshes